In a substrate processing step for semiconductor wafers and liquid crystal substrates, the substrate processing needs to be performed in a substrate processing apparatus under an environment with dust reduced in order to prevent occurrence of defects at the substrate processing. Dust within the substrate processing apparatus is reduced by supplying the substrate processing apparatus with clean air from which dust is collected by a filter.
Moreover, in the substrate processing step, the temperature of the processing environment is increased to activate the processing reaction and increase the processing speed, so that the productivity is increased.
To this end, a hot air generator for generating hot air is provided separately from the substrate processing apparatus. The hot air generated by the hot air generator is supplied to the substrate processing apparatus, and dust contained in the hot air supplied to the substrate processing apparatus is collected using a filter. The hot air generator includes: a casing; a heater accommodated in the casing; and a fan supplying air into the casing. In addition, an air duct is connected between the hot air generator and the substrate processing unit, and a filter collecting dust is provide to the air duct on an entrance side of the substrate processing apparatus.
On the other hand, instead of such a hot air generator provided separately from a substrate processing apparatus, another type of known system configured to supply hot clean air into the substrate processing apparatus includes a fan filter unit including a fan, a heater, and a filter and being installed above the substrate processing apparatus.
The method in which the hot air generator and the substrate processing apparatus are provided separately from each other and the hot air generator generates and supplies hot air to the substrate processing apparatus through the air duct, however, requires a space to install the hot air generator. Accordingly, the whole system including the substrate processing apparatus and the hot air generator requires a large space for installation.
In the case where the hot air generator is connected to plural substrate processing apparatuses, the lengths of the air ducts connecting the hot air generator and the substrate processing apparatuses differ among the substrate processing apparatuses in some cases. Such a difference in length among the air ducts easily causes temperature variations in the hot air supplied to the substrate processing apparatuses. If the hot air supplied to the substrate processing apparatuses has temperature variations, semiconductor wafers or the like processed by the substrate processing apparatuses vary in quality.
On the other hand, if the fan filter unit including the heater is used, heat of the heater is easily transmitted to the filter. Since the heat-resistant temperature of the filter is about 60° C., the heat transmission of the heater to the filter causes degradation of the filter due to deformation or the like, and therefore lowers the dust collecting performance of the filter.